The present invention relates to a system for regulating pressure in a process enclosure or chamber pumped by a vacuum pump unit for manufacturing and treatment processes concerning semiconductor components or micro- or nano-technology devices.
In industrial processes for manufacturing and treatment of such products in process chambers or enclosures fed with treatment gas at very low pressures, it is necessary to regulate the pressure inside the enclosure. Very low pressures, of the order of 1 Pa to 20 Pa, are obtained and maintained by a vacuum system which generally comprises a pump unit (a primary pump and a secondary pump) and pipework for connecting the process chamber to the pump unit.
There are numerous contamination problems in the various processes for manufacturing semiconductors or micro- or nano-technology devices. Some relate to the vacuum system which extracts gas from the process chambers and more precisely they relate to pumping conditions. A system for regulating pressure in the enclosure containing the manufacturing substrate (the process chamber) ought to provide a solution to some of this contamination.
When a chamber is pumped out, the gas in the chamber expands, thereby causing the gas to cool. If the pressure is lowered too quickly, then the temperature of the gas drops and a phase change is initiated (gasxe2x86x92liquid, gasxe2x86x92solid). Droplets or particles form in the pipework and in the chamber (on the substrate). They can diffuse back from the pipework into the chamber and thus increase contamination of the chamber.
If pressure is lowered quickly, then turbulent motion is generated. Such turbulent structures tear away particles that have been deposited in the pipework and the chamber, transports them, and redistributes them in zones that can be critical (on substrates where integrated circuits are being made).
A known method of regulating pressure in an enclosure being pumped out by a vacuum pump is to use a valve of variable conductance in series with the suction of the pump thus making it possible to vary the flow that is pumped and hence the pressure in the enclosure. The extent to which the valve is opened is adjusted by the control signal coming from a regulator circuit operating on the basis of a reference pressure and of the pressure measured in the enclosure.
That structure with a variable conductance valve is expensive and bulky.
In addition, the regulator valve positioned immediately at the outlet from the chamber to regulate pressure in the chamber at given gas flow rates nevertheless presents a large surface area for receiving deposits of particles generated by the processes and also by any degassing and desorption. By back-diffusion, desorbed particles can in turn contaminate the process chamber, thus reducing the reliability of the process. The presence of the valve increases and complicates maintenance operations in which it is necessary periodically to clean the vacuum system to remove deposits of particles generated by the processes.
The variable conductance valve also presents inevitable mechanical inertia which increases the reaction time of the vacuum system. In practice, a vacuum system having a variable conductance valve has a reaction time of at least about 5 seconds to cause the pressure in the process chamber to pass from one value to another in the usual pressure range of 1 Pa to 20 Pa between two steps in the process.
Another known method is to use a mechanical primary pump whose speed of rotation is variable and servo-controlled to a pressure gauge. However, the range of pumping flow rates that can be controlled is too restricted for semiconductor applications. As a result, at high vacuums, pressure regulation is not effective and contamination can develop.
In the field of semiconductor manufacture, document DD 262 065 A teaches using a vacuum system comprising a primary pump followed by two Roots type secondary pumps in series. The primary pump is a rotary vane pump driven to rotate at constant speed. The Roots secondary pumps are controlled by a microcontroller via variable frequency power supplies to modulate their speeds of rotation and thus to vary the pressure in the process chamber. The document states that this makes it possible to vary pressure over a range of 10 Pa to 100 Pa. The system is not suitable for providing effective control over pressure in a pressure excursion range going up to atmospheric pressure, and it does not enable reaction times to be obtained that are shorter than those obtained by vacuum systems having variable conductance valves.
One of the objects of the present invention is to increase significantly the range of controllable pumping rates in order to be able to regulate pressure over all process steps in semiconductor and micro- or nano-technology applications.
Another object of the present invention is to increase the reaction speed of the pumping system during transitions between successive process steps. In particular, it is desired to obtain reaction times that are clearly shorter than those of vacuum systems having variable conductance valves.
To this end, the invention relates to a system for regulating the pressure in an enclosure that is to contain process gas for manufacturing semiconductor components or micro- or nano-technology devices, the enclosure being connected by pipework to a pump unit comprising a dry mechanical primary pump and at least one secondary pump;
according to the invention, the system comprises a speed controller controlling simultaneously the speeds of rotation both of the dry mechanical primary pump and of said at least one secondary pump.
In an embodiment of the invention, the speed controller is servo-controlled to predetermined rotary speed profiles for the pumps calculated on the basis of condensation curves for the effluents contained in the enclosure and the pipework.
Advantageously, on its own or in combination with the condensation curves, the speed controller can also be servo-controlled to predetermined rotary speed profiles for the pumps, calculated on the basis of aerodynamic characteristics for non-turbulent flow of the effluents in the enclosure and the pipework.
In another embodiment of the invention, the system comprises:
a pressure gauge mounted upstream from the controlled secondary pump to monitor pressure; and
an observer receiving an input value proportional to the monitored pressure and an input value proportional to a variable reference pressure, and outputting a control signal to the speed controller to increase or decrease the speeds of rotation of the pumps as a function of its input values.
Advantageously, the system may comprise a temperature probe mounted upstream from the controlled secondary pump to monitor temperature, the observer receiving an input value proportional to the monitored temperature.
In addition, the system may comprise a turbulence sensor mounted upstream from the controlled secondary pump to quantify the degree of turbulence, the observer having an input value proportional to the quantified degree of turbulence.
The invention also relates to vacuum pumping apparatus comprising a pump unit having a dry mechanical primary pump and at least one secondary pump, a vacuum enclosure, and pipework connecting the vacuum enclosure to the pump unit.
According to the invention, the pump apparatus comprises a pressure regulator system as described above.
The secondary pump, controlled simultaneously with the dry primary pump, may be a turbomolecular pump.
The secondary pump, controlled simultaneously with the dry primary pump, may be a Roots type pump. In which case, a turbomolecular pump can be interposed between the controlled Roots type secondary pump and the regulated pressure enclosure or process chamber.
One of the advantages of the present invention results from simultaneously servo-controlling the primary pump and at least one secondary pump in the pump unit. This makes it possible to obtain a controllable pumping flow rate range covering 10 sccm to 10,000 sccm (0.16 millibar liters per second (mbar l/sec) to 166 mbar l/s) covering the needs of semiconductor applications. This also makes it possible to reduce significantly the reaction time of the vacuum system.
In a particularly advantageous embodiment, the observer is programmed to produce a variable speed control signal which, on receiving a step in reference value, presents a reaction time of less than 5 seconds and an overshoot of less than 5% during steps in the treatment of semiconductors or micro- or nano-technology devices in the enclosure.
For example, the observer is programmed to act via an open loop during the transient step of the process, and to act via a closed loop during steady conditions of the process.
This considerably reduces the reaction time of the system, enabling it to react considerably faster than is possible with vacuum systems including a variable conductance valve.